the milky way - sjsu

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The great tragedy of science – the slaying of a beautiful hypothesis by an ugly fact.

-Thomas Huxley

Monday, October 3, 2011

The Origin of Modern Astronomy

Chapter 4


I. The Roots of Astronomy A. Archaeoastronomy B. The Astronomy of Greece C. Aristotle and the Nature of Earth D. The Ptolemaic Universe

II. The Copernican Revolution A. Copernicus the Revolutionary

B. De Revolutionibus C. Galileo the Defender D. The Trial of Galileo

III. The Puzzle of Planetary Motion A. Tycho the Observer B. Tycho Brahe's Legacy C. Kepler the Analyst D. Kepler's Three Laws of Planetary Motion E. The Rudolphine Tables

IV. Modern Astronomy

Outline


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Ancient Greek Astronomers

Earth’s shadow is round as seen during an eclipse


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7°

7°

Eratosthenes (~ 200 B.C.):Calculation of the Earth’s radius


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Scale of the Solar System

Size of the Earth + Lunar Eclipse Observations

Size of Moon!!!


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Size of the Moon + Angular Size in Sky

Distance to Moon!!!


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Distance to the Moon + Sun/Moon Angle

Distance to Sun!!!


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Distance to the Sun + Angular Size in Sky

Distance to Sun!!!


Structure of the Solar System

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Geocentric Models


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Geocentric Models• Eudoxus (409 – 356 B.C.):

Model of 27 nested spheres


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• Aristotle (384 – 322 B.C.),

major authority of philosophy until the late middle ages: Universe can be divided in 2 parts:


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• Aristotle (384 – 322 B.C.),


1. Imperfect, changeable Earth,


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• Aristotle (384 – 322 B.C.),


1. Imperfect, changeable Earth,

2. Perfect Heavens (described by spheres)


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The WanderersPlanet: from Greek πλανήτης αστήρ planētēs astēr "wandering star"


http://en.wikipedia.org/wiki/Ancient_Greek


http://en.wiktionary.org/wiki/%CF%80%CE%BB%CE%B1%CE%BD%CE%AE%CF%84%CE%B7%CF%82


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Retrograde (westward) motion of a planet occurs when the Earth passes the planet.

The Wanderers

Motion of the planets across the sky is markedly different than the motion of the stars.

Planet: from Greek πλανήτης αστήρ planētēs astēr "wandering star"






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Refinements to Geocentric Models

Ptolemy’s epicycles(150 AD)

Model survived until Copernican Revolution of 1500’s.

Publication: Syntaxis (the greatest)


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Middle Ages

Islamic Period: 700-1300 AD

• High regard for the science• Religious motives for accurate timekeeping and astronomical observations• Translated Greek texts into arabic• Ptolemy’s Syntaxis (arabic: Almagest)

Contained a catalogue of > 1,000 starsAll were given arabic names

• Measured 23.5 tilt of Earth’s rotational axis with great precision.


Stellar Parallax


Stellar ParallaxWe can judge distances to objects because we observe the world through two vantage points -- two eyes.


Stellar Parallax

Greeks assumed the Earth was not moving because they did not observe parallaxes in the sky.

We can judge distances to objects because we observe the world through two vantage points -- two eyes.


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Parallax angle of the nearest star is less than 1/3600 of one degree.

Ancient astronomers tried to measure parallax via careful naked-eye observations but failed.

Finally detected in 1830 by F. Bessel using telescope.

Stellar Parallax


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We want to put a telescope on one of the planets to measure the parallaxes of stars in our galaxy. Would it be better to put the telescope on Mercury or Mars? Why?


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